The invention relates to a process for fabricating image sensors and other electronic devices for use in the image input section of facsimiles, digital copiers, image scanners and other image forming apparatus. Also, the invention relates to an image sensor.
Image sensors are used in facsimiles and other image forming apparatus to read image information. With a view to realizing a compact system, active efforts are being made to develop "contact image sensors" which do not use a reducing optical system but which are placed in proximity to the document surface so as to read the image on it. A contact image sensor of the type contemplated by the present invention comprises an insulating substrate carrying an array of light-receiving elements of a sandwich or other type that are formed by a thin-film stacking process and the electric charges generated in each of the light-receiving elements are sequentially extracted on a time basis by means of drive ICs provided in the neighborhood of the insulating substrate, thereby producing an image signal. A typical example of the conventional contact image sensor is shown in FIG. 10. A plurality of linear sensor arrays 11 are formed on a large-size insulating substrate 1 by a thin-film process and, thereafter, the substrate 1 is cut along lines 2 parallel to the sensor arrays 11, thereby yielding contact image sensors formed on separate rectangular sensor substrates 3. In order to reduce the number of drive ICs (not shown) that need to be used with contact image sensors of the configuration described above, it has been proposed that the sensor arrays 11 be grouped in more than one block whereas the light-receiving elements that compose each sensor array are matrix connected to the drive IC for each block by means of a multi-layer wiring 13 via a switching element array 12 composed of thin-film transistor elements that are associated with the individual light-receiving elements. According to the proposal, the electric charges generated by a light current in the light-receiving elements composing each block are transferred temporarily to the wiring capacity in each multi-layer wiring by selectively conducting the thin-film transistor elements for each block, and the transferred stored charges are read with the drive IC on a time basis, with the same sequence of operations being repeated for each block.
Since a plurality of contact image sensors are formed on the large-size insulating substrate 1 by a thin-film deposition process, the apparatus for implementing the process requires standardization of not only the outside dimensions of the substrate but also the area 4 where sensors and other patterns can be formed. In order to allow a certain width for each sensor array 11 while assuring efficient formation of more than one sensor substrate 3 from the single large-size insulating 1, an I/O port (input/output area) 20 having wirings for connection to an external drive IC is provided at one end of each sensor substrate 3.
However, each I/O port 20 has many wirings (e.g. signal lines that are equal in number to the light-receiving elements composing one block, gate control lines in thin-film transistor elements that are equal in number to the blocks, and bias voltage supply lines), so it has been necessary to form those wirings in three sides of an end of each sensor substrate 3 as shown in FIG. 10. This will inevitably yield sensor substrates 3 each having a pattern-free area 5 where nothing is formed by a thin-film process. The existence of such pattern-free areas 5 has eventually presented the problem of increasing the width of each sensor substrate 3 in a direction normal to sensor arrays 11, thereby reducing the number of sensor substrates 3 that can be taken from the large-size insulating substrate 1.